The requirements upon the quality of gunite built-up on metallurgical unit linings have grown to be more stringent.
There is known a flame guniting lance (German Pat. No. 2,200,667, issued on May 13, 1976) which consists of a water-cooled casing formed with ducts for supplying a powdered refractory material mixed with fuel and for admitting oxygen, whereby the refractory material, heated to a plastifying state in a high-temperature flame, is deposited on the lining surface. The water-cooled casing and the ducts for supplying the powdered refractory material mixed with the fuel and oxygen are bent through an angle of 15.degree. to 30.degree. with respect to the plane perpendicular to the axis of a nozzle which situated at the end face of the ducts, is directed at the right angle thereto. This constructional arrangement ensures good adhesion of the refractory material to the surface of a metallurgical unit lining.
However, the practical application of this lance for flame guniting involves problems. The sole nozzle adversely affects operating efficiency of the lance, the flame spraying operation being time consuming.
In addition, the curved shape of the lance complicates its manufacture and hinders the manipulations necessary to carry out while introducing the lance into, and pulling it out of, a metallurgical unit.
It should also be noted that the curved-shaped ducts for supplying the mixture of the powdered refractory material and fuel are subject to heavy abrasive wear, this substantially reducing the service life of the lance.
It should be noted that the powdered refractory material, fuel and oxygen are intermixed only after they exit from the respective nozzles. Since the refractory-fuel mixture and oxygen are supplied in parallel jets, their intermixing proceeds at a very slow rate, with the flame extending over a considerable distance from the nozzle. As the water-cooled casing and the concentric ducts formed therein are made curved in shape, the flame is directed tangentially relative to the surface of a metallurgical unit lining with the effect that the refractory material particles lack sufficient force of adhesion to ensure their reliable sticking to the lining. As a result, a considerable amount of the finer fractions of the powdered refractory material are entrained by the outgoing gases.
Another known lance for flame guniting (Metallurgy Journal No. 12, p.p. 25-26, Metallurgia Publishers, Moscow, 1977) consists of a water-cooled casing formed with concentrically arranged ducts for supplying a mixture of a refractory material and a fuel and for supplying oxygen. The powdered refractory material fuel mixture and oxygen are injected through several nozzles (for example, five) perpendicularly to the surface of a metallurgical unit lining. The lance of this type is simple in construction and reliable in operation owing to the fact that the ducts and the water-cooled casing are not curved. Projecting the flame at a right angle to the metallurgical unit lining makes it possible to slightly improve the quality of the refractory coat.
Despite certain advantages of the above lance over the single-nozzle curved lance, it still holds no answer to the problem of enhancing the degree of utilization of the refractory material deposited upon a lining and thereby producing high-quality refractory coat.
The refractory material-fuel mixture and oxygen are supplied in this type of lance in parallel jets, with the effect that mixing is very slow. As a result, the refractory material-fuel mixture and oxygen are intermixed to be ignited immediately before impinging upon the lining of a metallurgical unit. The fuel combustion begins in the zone of flame impingement and continues as the flame moves along the lining. As a result, a part of the refractory material is not heated to a plastifying state and thus fails to form a strong bond with the lining. This, in turn leads to a certain amount of the refractory material carried out of the metallurgical unit with combustion gases.